New study unravels the response of aquatic carbon dioxide and methane to flooding

New study aquatic carbon dioxide and methane to flooding.jpg

August 2016 Author Jackie Webb

Capturing the impact flood events have on carbon emission from aquatic systems is an important aspect of carbon cycle research, particularly if we want to understand how ecosystem carbon budgets may change based on future predictions of more frequent and intense rain events. Yet very little is understood on the biogeochemical drivers of carbon dioxide (CO2) and methane (CH4) after flood events. This paper presents a high temporal resolution study of dissolved CO2 and CH4 dynamics following a flood event in the artificial drains of a coastal floodplain. Using a natural geochemical tracer for groundwater (radon-222), the contribution of groundwater to total drain fluxes was found to be large for CO2 yet negligible for CH4. The extreme CO2 supersaturation observed in this study was four to eight-times higher than other recorded post-flood CO2 responses, and was sustained by large inputs of high carbonate alkalinity groundwater into acidic surface waters. In contrast, drain sediments were the major source of CH4, the response of which was driven by hydrological residence time. Carbon stable isotopes of CH4 (δ13C- CH4) and dissolved oxygen saturation levels revealed a strong diurnal control over post-flood drain CH4 dynamics. Findings from this study reveal how major drivers in CO2 and CH4 dynamics can operate on different hydrological and biological scales, and how the unique geochemistry of certain coastal floodplains can have a profound influence over post-flood fluvial CO2 and CH4 emissions.